Mind and Body, Medieval and Modern: Augustine and Thomas Aquinas Versus Descartes
by David McGraw
Part II
Saint Thomas Aquinas stood with Augustine on many key points concerning the nature of reality. This includes important points where he stood with Augustine and against Descartes on issues having to do with the specific problems of mind and body. Thus, Aquinas agreed with Augustine that matter sits at the bottom of the hierarchy of the universe. He agreed that a rational creature is superior to a dead body because God gives more to the one than to the other. Aquinas agreed that to be spiritual is to have levels of power and perfection that go beyond what can be captured within matter. He agreed that the human soul comprehends but does not exemplify extension; or rather, the soul exemplifies extension by developing and maintaining the body but not within itself. Aquinas agreed that this is so because the human soul (like God, or an angel) is superior to what does exemplify or display extension within itself. Again, he stood with Augustine against Descartes in affirming the basic division between sense and intellect, with all that this division entails for both the human subject and the nature of reality. For all these reasons, Aquinas stood with Augustine in understanding the situation of mind and body better than Descartes.
However, Augustine agreed with Descartes in speaking of the soul as numerically separate from the body and all its parts, although very differently from the way Descartes understood this thesis. Unhappily, given this separation, there is no way to avoid the enormous, and notorious, challenges that have been brought against Cartesian dualism. This point applies to Augustine's version as well.
These challenges are so severe that the strongest reason for saying materialism is true of the human person may be phrased as a modus tollens argument. "If materialism is not true, then Cartesian dualism is not false. But Cartesian dualism is clearly false and obviously absurd. Therefore, materialism is true." This conclusion does follow, and the criticism of Cartesian dualism is certainly correct. Consequently, materialism is often accepted as the only theoretical framework worth taking seriously.
But there is another possibility. One can deny materialism apart from affirming Cartesian or even Augustinian dualism. Long before Descartes, there was what might be called the theory of the "top down" structure of the human subject. The origins of this theory go back to ancient times. This theory is what Aquinas followed.
This "top down" theory is something like a dualism of attributes within a single substance. But this substance is really more mental than material or corporeal. For it is not correct to say that mental attributes belong to the body. The truth is almost exactly the opposite. This theory is much more like Strawson's idea of the person, with mind and body together, as the primary unit. However, the sort of personalism proposed here has the mind as the dominant factor within the person. To speak in a picturesque metaphor, one could almost say the mind reaches down to include the body, and this complex of mind and body is the human person. Perhaps the chief fault of this metaphor is that the mind does not so much reach down as though it were exercising strength. Instead, it would be better to say that the (human) mind spills down or lapses into matter because of its natural weakness. (The human soul is "weak" as needing to be involved with matter instead of being able to stand alone as a pure spirit.) Thus, this theory is almost like idealism, since the body may be said to be a function of the mind, except that the body is fully real. More properly, this theory is to idealism (more or less) what traditional epiphenomenalism is to materialism. For this reason, one might speak of this theory as "reverse epiphenomenalism," and this theory has been spoken of in this way on this basis.
Thus, Descartes was right to speak of himself as a thinking thing. But whether thinking allows or excludes extension as an attribute is a separate question. The thing that thinks might turn out to be material, or spiritual, or some sort of hybrid. What is proposed here is that the thing that thinks (the “rational substance”) is a kind of hybrid. Intellect and will belong to the inner spirituality of the person, and this inner spirituality is a level or layer within someone that is above the material. On the other hand, the spiritual soul of the human person is also the "organizing and architectonic principle" of the living animal body. The thing (or “substance”) that is the person is then the rational animal as a living being.
This theory may be explicated more fully by going into its historical development. Plato argued against materialism, but he also affirmed full dualism. However, Plato also said that the soul weaves the body around itself. This statement is too clearly metaphorical to be more than merely suggestive as it stands. Then again, one must presumably say that the body is derived from the functioning of the soul instead of having the mental life of the person be developed out of the functioning of the body. If it means anything at all to say the soul weaves the body around itself, it has to mean at least this much. This kind of reverse epiphenomenalism is the third alternative, apart from both materialism and dualism. Plato combined this thesis, that the soul develops and maintains the body, with full dualism. But these theories can be distinguished.
After Plato, Aristotle spoke of the soul as the form of the body. What he meant by this idea may be subject to interpretation. On the other side, Aristotle argued against materialism as regards the thinking mind. If he had said the thinking mind is part of the human individual, then he might be committed to saying the soul develops the body. As it is, what Aristotle believed about the thinking mind may also be subject to interpretation. In any event, Aristotle gave the chief dignity to form over matter. A thing's form is the principal basis for the thing to be what it is and to do what it does. So, Aristotle's answer seems to be that the soul develops the body instead of being derived from the body as an epiphenomenon.
This theory was clearly the answer given by Thomas Aquinas. Like Plato and Aristotle, Thomas Aquinas argued against materialism on the ground that reasoning transcends matter. But he also opposed full dualism. Instead, Saint Thomas said that the soul is the chief active principle within the person. There are intellectual capabilities because there is more to the (human) soul than what is involved in being the organizing and architectonic principle of the body. Abstract thinking belongs to this superior level within the person.
This theory seems to be the best available answer regarding mind and body. One of the strongest reasons in favor of this theory is that it has the most serious advantages of Cartesian dualism, but escapes the four chief objections. This point will be demonstrated by examining each of these four objections in turn.
To begin with, there are two obvious problems concerning individual identity. First of all, there is the problem of individual identity as regards diversity from others. For one must ask in what ways things are differentiated to be numerically separate from each other. As Aquinas pointed out, God is diffferentiated from other things by the very fact that He is infinite and they are finite. Things other than God can be differentiated from each other in some material way, or by differing in kind or species, or perhaps in both ways. (Two dogs differ from each other in virtue of material facts, or material stuff, or both. A dog differs from a cat in kind or species, and that fact would be enough by itself to establish them as separate beings.) That is all.
Along this line, Thomas Aquinas spoke of angels as (created) pure spirits. But in order to do this, he had to say that each angel differs in kind or species from every other angel. Only in this way can one angel be numerically diverse from another. An angel is created and so is not God. Since angels have no material stuff in them, and no material restrictions upon them, there is only the difference in kind or species to make them separate from each other.
Now, if the human mind were truly a separate substance from the body, it would presumably be a pure spirit in the manner of an angel. So, if there were to be a multitude of separate human minds, then they would all have to differ in kind or species from each other. But in fact, the available evidence points very strongly in the opposite direction. Therefore, the evidence is clearly against dualism.
On the other hand, this argument fails to reach the kind of "top down" personalism proposed here in anything like the same way. A human person is a sort of material substance, even though it is also much more than this. Thus, a human person is fully subject to multiplicity within the same species, like any other animal but unlike an angel.
Second, there is a problem of individual identity as regards continuity through time. What happens when someone falls into a deep coma, so that there is no mental life at all going on inside the person? A dualist must either insist that mental life does not fully cease even in deep coma or admit that the person's life has lapsed in such cases. Either of these answers is at least seriously questionable given the available evidence.
For Aquinas, the answer is clear enough. Mental dispositions can exist apart from being exercised, just like any other dispositions. (For example, a man can be intelligent even when he is not thinking, just as a lump of salt or sugar can be soluable when it is not presently being dissolved.) Even if the person “could not be” restored to having mental life, this would show only that the impediments to natural functioning could not be removed by the available healing arts. The person would still exist as a rational substance. Moreover, it would be false to say that the person is then a substance with no qualities or events actually present. So long as there is bodily life, the qualities that arise out of bodily functioning belong to the person, since the nature of the distinctively human person includes the body. These bodily qualities and events are enough for the life of the person to continue as something actually occurrent.
To be sure, this second problem weighs much less heavily on Augustine than it does on Descartes. The reason is that Augustine was much more concerned than Descartes to affirm that the soul develops and maintains the body. Therefore, Augustine could stand with Aquinas and say that, in such cases, the soul is still exercising vital functioning over the body, even though no mental life is presently being exercised.
Third, there is the problem about how the mind of a human person works. Once again, if the human mind were truly a separate substance from the body, it would presumably be a pure spirit in the manner of an angel. In that case, the mental life of a human person would presumably be free from any weaknesses or limitations derived from matter. But this is clearly false. Moreover, such weaknesses and limitations, so far from being externally imposed on the mind, appear to derive from the inner nature of the mind. Furthermore, these restrictions seem to reach even those distinctive operations of intellect and will with the strongest claim to transcend matter. Thus, once again, full dualism appears contrary to the available evidence.
On the other hand, the theory proposed here is fully compatible with all this evidence. A human person looks very much like an animal with some distinctively spiritual capabilities laid on top of its nature as an animal. The reason is that this is what a human person is in fact. Intellect and will exist only in conjunction with the person's nature as an animal, even though they transcend this nature. For this reason, abstract thinking and deliberate choice occur only within the context defined by someone's life as an animal (where this life is taken to include imagination and emotion as well as sensory perception). All this remains so even though these activities are ultimately irreducible to any kind of purely animal functioning.
What this involves can be illustrated from the specific concerns over visual experience. Aquinas agreed with Augustine that the soul to which intellect and will belong is the same soul that animates the body. They agreed also that the soul is nonspatial, albeit as transcending spatial restrictions and not as lacking anything. But then it seems mysterious how the soul can accommodate the vast spaces that show up in visual experience. Augustine answered that this is so because of the soul's superior power. Aquinas would (almost) agree, but in a different way.
Saint Thomas considered that, properly speaking, it is the human person to which mental life belongs, rather than the soul as such. Along this line, the soul's superior power allows the spaces that show up in visual experience to be accommodated by establishing and holding the body as an integral part of the person. Insofar as something literally spatial is needed to accomodate these spaces, this something is present, and it is the body of the person. Sensory experience (visual or otherwise) is a function of the body, just as abstract thinking and deliberate choice are functions of the spiritual soul. But since body and soul together make up the human person as a single unit, these functions are combined to make up the mental life of the person as something unified.
What if it were to be proposed that the soul itself is literally spatial? The answer to this proposal involves going back and considering a prior question. Why should one affirm any soul in the first place, instead of just attributing mental life to the body? One answer is that self aware consciousness seems to require something deeply unified as the subject to which it belongs, and the body is not sufficiently unified. Descartes seems to have been right about this. But then the soul cannot itself be spread out in the same way as the body, or there would be the same problem all over again. This "top down" theory provides for Descartes's insight but avoids the problem about experiencing space.
Fourth, and most notorious, there is the problem about interaction. Even if there could be a separate human mind with the required attributes, one would still have to ask how it is related to the body. Since mind and body are supposed to be fully constituted substances, they would have to interact causally. No mechanism for such interaction is even minimally plausible. However, the basic problem is far deeper than this. The problem is that the theory turns out to be demonstrably incoherent as regards the body. For the body has to be a fully constituted substance, and yet it must be naturally ordered to receive causal influence from the mind. This influence appears not to be externally imposed on the body: it appears instead to fit right into the functioning of the body. Thus, the functioning of the body must be profoundly incomplete in some way to make room for this influence. But this result is contrary to the claim that the body is a fully constituted substance.
On the other hand, this evidence may even support the theory proposed here, for the body is not claimed to be a fully constituted substance within itself. Instead, the soul is the organizing principle of the body. The mental life of the human person can govern bodily activity by influencing how bodily processes are organized. There remains some question about the mechanism, but the basic problem of conceptual logic is eliminated.
Yet the body seems to be fully organized within itself as a material system. No spiritual activity appears to be required for the body to be what it is and do what it does as a body.
The answer to this objection depends on observing a fine distinction. The human body is organized within itself in the sense that the material system works out on its own terms as a material system. However, the body exists as a unified whole only because it is the body of some living person. The soul is the organizing and architectonic principle of the body, but not as though the body needed some magical glue to hold it together. Instead, the body is deeply unified and integrated as a living thing, instead of being a mere machine. The body is a unified whole in virtue of being alive. But the body is animated with the distinctive life of a person. Thus, the basis for the human body to exist and operate as a whole also includes capabilities that go above and beyond what belongs to the functioning of material things as material. It is in this way that the soul acts as the form of the body.
Will this answer work out? Paradoxically, it can be made to stand if materialism can avoid being absurd on its face. Any sophisticated materialism has to allow higher animals, and especially human subjects, to be more than machines. For mechanism cannot contain or support the mental life of a dog or a cat, let alone that of a man or a woman. The obvious answer is that all these are living beings instead of mere machines. But then this point about the advantage of being alive cuts both ways. Different types of beings may be alive in different modes and have various capabilities on that basis. In the case of the human subject, the mode in which the animal is alive turns out to be exalted enough to allow for even distinctively spiritual functioning. That is all. "Top down" personalism is vindicated on this basis.
Along this line, there is no substitution within the human person of spiritual activity for material functioning of the body. What has to be understood here is that the idea of "top down" structure is taken very seriously as regards the human person and indeed the nature of reality as a whole. Lower levels work out correctly on their own terms as far as may be, and higher levels work by means of lower levels as far as may be. In the present case, intellect and will cannot be wholly reduced to, or constructed from, the lower levels of the human person. (That is what it is for these faculties to transcend those lower levels.) But still, intellect and will work largely by means of emotion, imagination, sensory perception, et cetera. (A man may implement or promote the functioning of his intellect and will by imposing discipline on these subordinate functions, in terms of forming pictures in his mind, directing or calming his feelings, and so on.) Again, the work of imagination, et cetera, is accomplished by means of complex patterns and processes of neural functioning, and this functioning is accomplished by means of low level metabolism, and this metabolism works by means of "nitty gritty" electrochemistry, and so on right down to the underlying quantum physics (or whatever the truth turns out to be). At no point is there any substitution of higher level functioning for that of the lower level.
Given all this, one of the strongest arguments for materialism is easily answered. Yes, of course the activities of intellect and will are strongly correlated with neural electrochemistry. Since the higher levels of the person work by means of the lower levels as far as may be, what these higher levels do or fail to do will be largely influenced by what does or does not happen on the lower levels. Similarly, what the craftsman does or fails to do will be largely influenced by what does or does not happen to his tools. But even so, the craftsman is clearly superior to his tools. So here in like manner, intellect and will are superior to neural electrochemistry.
Then again, Saint Thomas can give this answer. What Descartes can say is much more problematic.